Jupiter
The largest planet in the solar system, and the fifth in the order of distance from the Sun. It is visible to the naked eye, except for short periods when in near conjunction with the Sun. Usually it is the second brightest planet in the sky; only Mars at its maximum luminosity and Venus appear brighter. Telescopic Appearance Through an optical telescope Jupiter appears as an elliptical disk, strongly darkened near the limb and crossed by a series of bands parallel to the equator (Fig. 1). Even fairly small telescopes show a great deal of complex structure in the bands and disclose the rapid rotation of the planet. The period of rotation is very short, about 9 h 55 m, the shortest of any planet. The features observed, however, do not correspond to the solid body of a planet but to clouds in its atmosphere, and the rotation period varies markedly with latitude. Red Spot Apart from the constantly changing details of the belts, some permanent or semipermanent markings have been observed to last for decades or even centuries, with some fluctuations in visibility. The most conspicuous and permanent marking is the great Red Spot (Fig. 2), intermittently recorded since the seventeenth century and observed continually since 1878. At times it has been conspicuous and strongly colored; at other times it has been faint and only slightly colored. The Spot's distinctive coloration is probably due to chemical compounds (perhaps containing phosphorus) transported from deep within the atmosphere. The origin and longevity of the Great Red Spot remain difficult to explain. Atmosphere Jupiter's visible belts and zones reflect the complicated vertical atmospheric structure. The atmosphere consists primarily of hydrogen (H2), helium (He), ammonia (NH3), methane (CH4), water (H2O), hydrogen sulfide (H2S), and other trace compounds. In the simplest model, the deepest cloud layer consists of water vapor and ammonia cumulus clouds. These form a cloud bank about 16 mi (25 km) thick which is overlain by a 6-mi-thick (10-km) clear region probably saturated with gaseous ammonia. Above this are ammonium hydrosulfide (NH4SH) clouds, the tops of which perhaps receive a constant liquid ammonia rain from a higher level of ammonia clouds nearly 12 mi (20 km) in vertical extent. A high-altitude smog layer obscures the entire planet. The belts and zones represent regions of differing cloud altitudes and compositions. The atmosphere is divided by a series of prograding and retrograding jet streams. Convection is strong since the bright zones are cooler and higher by 9–12 mi (15–20 km) than the dark belts, with their higher albedos arising from solid ammonia crystals. Individual vortices form within the zones and belts, some persisting for decades. The major white ovals are hot-spot regions of strong infrared emission and are consistent with convective motion from the deep water-cloud layers, while other features such as the plumes observed in the equatorial region may be surface phenomena. During July 16–22, 1994, 21 observable fragments of Comet Shoemaker-Levy 9 impacted the Jovian atmosphere at nearly 120,000 mi/h (200,000 km/h), the first time such an event had been witnessed. Though occurring on Jupiter's nonvisible side, each strike was clearly visible as a dark area in the south temperate zone as the planet's rapid rotation brought it into view. In addition, ejecta and impact plumes were seen to rise approximately 1860 mi (3000 km) above the planetary limb. The event provided a first probe into the Jovian atmosphere. See also Comet. There is also some atmospheric beasts in the gasceous clouds. Interior composition and structure Jupiter primarily consists of liquid and metallic hydrogen. Early measures of the ratios of helium, carbon, and nitrogen to hydrogen gave values resembling those of the Sun, and therefore, the primordial composition of the solar system. However, later analyses of the methane spectrum showed a two- to threefold overabundance of carbon as compared to solar values, a result confirmed by gravity analyses of the rocky core. Still in a late phase of its gravitational contraction, the planet converts the released gravitational energy into heat, emitting 1.668 times as much thermal energy as it receives from the Sun. The cloud zone thickness actually extends only 0.1–0.3% of the Jovian radius. Beneath that, the atmosphere is clear and gradually metamorphoses into the liquid hydrogen molecular fluid envelope which makes up approximately the outer 20% of the radius. The transition at lower depths to metallic hydrogen is abrupt. See also Hydrogen. Observations suggest that the planet could be homogeneous (that is, it has no core) or else it has a dense central core with a mass less than or equal to 12 earth masses. The large abundance of carbon suggests that gases other than those from the solar nebula contributed to the composition of Jovian volatile gases. Probably the entire planet holds 11–45 earth masses of elements other than hydrogen and helium. Jovian Magnetosphere Jupiter possesses the strongest magnetic field and most complex magnetosphere of any planet in the solar system. This field rotates with the rotational period of the planet and contains an embedded plasma trapped in the field. At the distance of the satellite Io, the field revolves faster than the satellite, and so numerous collisions occur with the atmospheric gas of that body, resulting in the stripping away of 1028–1029 ions per second. The energy involved slows the magnetic field, and so, beyond Io, the magnetic field no longer rotates synchronously with the planet. The ions removed from Io spiral around the magnetic lines of force, oscillating above and below the plane of Io's orbit. This ring of ions is known as the Io plasma torus and emits strongly in the ultraviolet. The motion of Io through the magnetosphere creates a 400,000-V, 2 × 1012 W circuit, sufficient to cause pronounced aurorae in both the equatorial and polar regions of the satellite. Jovian ring Voyager 1 and 2 detected a faint ring encircling Jupiter. It appears to have three parts, which interact in a complicated, dynamic way with the planet's magnetic field and several embedded satellites. Satellites Jupiter has 63 known satellites of which the four largest, I Io, II Europa, III Ganymede, and IV Callisto, discovered by Galileo in 1610, are by far the most important. The four Galilean satellites are of fifth and sixth stellar magnitudes and would be visible to the naked eyeif they were not so close to the much brighter parent planet. They are easily visible in binoculars. All the others are faint telescopic objects. The close approaches of the Voyager and Galileo spacecraft as well as the superior imaging capabilities of the Hubble Space Telescope have shown the four galilean satellites to be very different. I Io is probably the most geologically active body in the solar system. Its surface landforms include active shield volcanoes, calderas, mountains, plateaus, flows, grabens, and scarps. Spacecraft have shown that Io possesses over 80 separate volcanoes. The source of this volcanism is thought to be the transformation of tidal energy into heat as Jupiter's gravity deforms the satellite surface by several hundred feet. Europa, primarily a rocky body, may be rich in silicates and lightweight water ices. The surface displays a satellite-wide system of cracks, and ridges, running for thousands of miles, about 10–25 mi (16–40 km) in width. There are few elevations, and the surface is remarkably free from craters. The ice surface makes the satellite one of the most reflective bodies in the solar system. Geologic activity is thought to heat the ice under the surface to near-liquid state, allowing it to gush through in volcanoes of slush and water. It is likely that liquid oceans exist on Europa at depths more than 6 mi (10 km) below the surface, kept liquid by geothermal activity and tidal action. This is suggested by the variable Europan magnetic field observed by the Galileo spacecraft. It is not inconceivable that simple life may exist in the Europan oceans, much in the same way as in Earth's oceans lifeforms congregate near thermal vents. The density of III Ganymede suggests that it is composed largely of ice. It has a metallic core approximately the size of Io, surrounded by a 500-mi (800-km) shell of rock and a similarly sized overmantle of ice. The surface formed recently since there are few large impact craters, but those that exist may have crater caps of frost. Since it is similar in radius and density, IV Callisto should have a geological history resembling that of Ganymede, but does not. In fact, it seems to have been geologically dead for millions of years. It is the most heavily cratered of the galilean satellites and has not undergone extensive resurfacing since the time of impacts. Native Lifeforms Jupiter is also home to strange creatures called atmospheric beasts and their habitat is the clouds. Their gas-based organism that thrive by feeding on the gases. The Jupiterians thrive in groups or they hunt for food. Category:Planets